1. Two teams are having a tug-of-war match. Which of the following can be considered an isolated system?
a) one team
b) both teams
c) both teams and the rope
d) none of the above (the earth is part of
the system!)
2. A railcar (mass of 1000 kg) moves horizontally at speed 10 m/s. Friction between the railcar and the track can be neglected. A 40-kg bale of hay falls vertically onto the railcar; the car continues to move horizontally.
How do the horizontal momentum and the kinetic energy of the railcar-hay system change, if at all, when the bale of hay falls into the car? (Assume that the vertical speed of the hay just before it lands in the cart is small enough to neglect its contribution to the system kinetic energy.) Choose all that are true.
a) horizontal momentum remains constant (the cart
loses the momentum and the hay gains it)
b) horizontal momentum increases
c) horizontal momentum decreases
d) kinetic energy remains constant
e) kinetic energy increases
f) kinetic energy decreases (it is a totally
inelastic collision so KE is lost)
3. Two objects with inertias m1 and m2 approach each other from opposite directions and collide head-on elastically. Object 1 leaves with a final speed greater than its initial speed. How do m1 and m2 compare?
a) m1 > m2
b) m1 = m2
c) m1 < m2
d) not enough information (it depends on the
relative speeds of the objects. If the initial speeds were the same then
the answer would be (c))
4. A basketball dropped (from rest) from a height of 1 meter strikes the earth and returns to a height of 1 meter. The collision between the basketball and the earth is:
a) elastic (mechanical energy is conserved)
b) inelastic
c) totally inelastic
d) explosive
e) not enough information
5. A toy truck with low-friction bearings is rolling on a flat, horizontal surface when a pebble is gently dropped into its bed such that the pebble’s horizontal velocity before landing in the truck is zero. Compared to the momentum of the truck before the pebble lands in the bed, the momentum of the truck and pebble after the pebble lands in the truck is
a) greater.
b) less.
c) the same (total momentum is conserved)
6. A toy truck with low-friction bearings is rolling on a flat, horizontal surface when a pebble is gently dropped into its bed such that the pebble’s horizontal velocity before landing in the truck is zero. Compared to the kinetic energy of the truck before the pebble lands in the bed, the kinetic energy of the pebble and truck afterwards is
a) greater.
b) less.(KE is not conserved in a totaly inelastic
collision)
c) the same.
7. An explosion splits an object initially at rest into two pieces of unequal mass. Which piece moves at greater speed?
a) The more massive piece.
b) The less massive piece. (they each have the
same momentum)
c) They both move at the same speed.
d) There is not enough information to tell.
8. An explosion splits an object initially at rest into two pieces of unequal mass. Which piece has greater kinetic energy?
a) The more massive piece.
b) The less massive piece. (KE =0.5 mv^2) if
you half m and double v then KE is double
c) They both have the same kinetic energy.
d) There is not enough information to tell.
9. A ball is thrown against a wall; it bounces off and returns with speed equal to its initial speed before striking the wall. Which of the following statements is true from before to after the collision between the ball and the wall?
a) The kinetic energy of the ball is conserved.
(the magnitude of momentum is equal but it is in the opposite direction
b) The momentum of the ball is conserved.
c) Both the kinetic energy and the momentum of the ball are conserved.
d) Neither the kinetic energy nor the momentum of the ball are conserved.
e) The collision is inelastic.